20 



HARDWOOD RECORD 



by loggiug or by hogs. A thick hiyor of dry leaves is unfavorable. 

 Seedlings and small trees of yellow poplar are extremely sensi- 

 tive to fire, being more easily injured even than chestnut. This 

 is duo primarily to the thin and smooth bark of the young tree 

 of yellow poplar. An additional reason for their great injury 

 is that tlie sap and inner bark of yellow poplar become active 

 earlier than in the associated trees. This greatly e.xposes this 

 species to early spring fires, which, when they take place during 

 dry and windy periods before the forest foliage is out, are very 

 hot and destructive. Fortunately yellow poplar is somewhat pro- 



tected by being largely confined to the damp hollows and coves. 

 Seedlings of yellow poplar which are killed dovra by fire will 

 usually sprout from the root, unless they arc shaded. 



Mr. Ashe estimates the yellow poplar timber still standing in 

 Tennessee at a,500,000,n00 feet, board measure. If the ratio of 

 annual cut to the amount of standing timber in Tennessee is taken 

 as a basis of estimate, it follows that the remaining stands of 

 this timber in the United States is approximately 14,000,000,000. 

 At the rate of cutting in 1911 tliis is a supply for twenty-one 

 years. 



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Wood in Relation to Heat 



Wood owes its popularity for certain uses to the fact that it is 

 a very poor conductor of heat. Imagine the result of substituting 

 metal for wood in the manufacture of matches. The user would 

 need asbestos gloves to handle them. It is due to this poor heat 

 conductivity of wood that shingles have one decided advantage 

 over other roofing materials. Anyone who has slept directly under 

 a tin roof following a hot day can vouch for this statement. 



This also has a bearing on the substitution of steel for wood 

 in making filing cabinets. It is quite true that the steel will not 

 burn, but this property of metal is not sulEcicut to guarantee the 

 protection of the paper in the cabinet. If a building is entirely 

 consumed, nothing but a first-class safe or vault can be expected 

 to pass through the ordeal with its contents uninjured. In the 

 case of smaller (ires that are extinguished a thin-walled filing 

 cabinet offers less protection to its contents than one made of wood, 

 because immediately after the first contact of the flames with the 

 metal it becomes hot enough inside to scorch the papers. Later the 

 buckling and warping of the case will permit enough air to cause 

 the contents to burst into flames. Where wood is used the con- 

 tents are safe until the wood burns through — a considerably longer 

 time than when steel or sheet iron is used. 



Fire damage to structures is by no means confined to the actual 

 burning. Buildings of stone, brick, steel and concrete are non- 

 combustible but this does not prevent their serious damage and 

 possible collapse due to fire. Where iron girders are used in build- 

 ings, in case of the structure being burned, the expansion of the 

 girders tends to shove down the walls; this is not the case with 

 wooden beams because the coefiicient of linear expansion of woo<l 

 due to heat is very small. 



By coeflieient of linear expansion is meant the increase in its 

 length for each degree rise in temperature, divided by the original 

 length of the specimen. For oak this coeificient has been found 

 to be .00000492. The coefficient of radial expansion for oak is 

 .0000544, or about eleven times the longitudinal. Spruce expands 

 less than oak and the ratio of longitudinal to radial expansion is 

 only six to one. Metals and glass expand equally in all directions 

 since they are homogeneous substances, while wood is a compli- 

 cated structure. The coefficient of expansion of iron is .0000285, 

 or nearly six times the coefficient of linear expansion of oak and 

 seven times that of spruce. 



The expansion of wood due to heat can be determined only when 

 both the wood and the air in which it is placed are absolutely dry. 

 Otherwise the heat drives out the water and causes a shrinkage 

 that not only counteracts the expansion due to the heat, but 

 may even produce a reduction in volume. Since wooden beams and 

 girders always contain at least a small percentage of water, the • 

 occurrence of a fire would not cause any appreciable expansion at 

 all. In the case of metal, however, the question of contraction and 

 expansion with changes in temperature presents many serious prob- 

 lems that cannot always be overcome. 



Fire-proof construction is not determined entirely by the com- 

 bustibility of the material of construction. Even more important 

 are the nature of the contents, the design of the structure, and 

 the precautions taken against fire. When the entire contents of 



a building are consumed, possibly including loss of life, it is 

 rather small consolation to know that the blackened structure still 

 stands. As a building material for houses in the less crowded 

 areas, by far the larger percentage of all houses built, wood is 

 a convenient and excellent material and the fire damage is little 

 if any increased by its use. 



It is by no means so easy to destroy a large wooden beam, post 

 or girder by fire as many people think. Finely divided wood 

 burns rapidly but large solid or closely bolted sticks of most 

 woods show great resistance even to intense and continued heat. 

 The surfaces char readily but owing to the fact that wood is a very 

 poor conductor of heat the inner portions remain intact and strong 

 for a much longer time than is commonly supposed. Heat in- 

 creases the pliability of wood only when special precautions are 

 taken to retain the moisture. Hence a wooden beam or support, 

 unlike metal, will not soften and thereby buckle and bend when 

 heated, even though the surface is glowing. 



Not enough attention has been devoted to the important ques- 

 tion of making wood more fire resistant by chemical treatment. 

 Although there are many patented processes on the market only 

 a very small proportion of structural timber is fireproofed. One 

 of the principal reasons for this is the cost and the inconvenience 

 of treatment. It is also claimed that certain processes increase 

 the hygroscopicity of wood, interfere with ease of working with 

 tools, and cause paint to scale off. It is interesting to note the 

 recent increased interest in this work which offers such a fruitful 

 field. S. J. R. 



The Boxes Come Back 



The Chinese are shipping eggs to this country in large numbers, 

 and some of them are in the markets as far east as the Mississippi 

 river. The eggs are stamped, each with Chinese letters, which 

 are supposed to be a certificate of freshness. An interesting 

 feature of the shipment of eggs from the old world to this is 

 that they come in American-made boxes. The shooks are man- 

 ufactured in Washington, Oregon, and California and are sold 

 in China for the egg trade. For a time the eggs went to England 

 and other European countries, but the ever-watchful Chinese saw 

 a chance in America and they were quick to take advantage of 

 it. There is food for reflection in the fact that the Chinese can 

 buy boxes 6,000 miles away, fill the boxes in the interior of their 

 country with eggs, and .ship them 8,000 miles to the Mississippi 

 valley, and there undersell the eggs produced in Missouri, Iowa, 

 and Illinois. The boxes must pay freight on at least 14,000 miles 

 of carriage by land and sea.. 



Practically the same thing has long been occuring with tea 

 boxes. It was formerly customary for tea merchants in Scotland 

 to buy yellow poplar lumber in the United States, transport it 

 to Glasgow, there manufacture it into shooks and send them to 

 China, where the Chinese completed them and covered the outside 

 with paper and inside with tin foil. Many of these boxes came 

 back to the United States filled with tea. The custom has not yet 

 wholly ceased. 



